1. Field of the Invention
The present invention relates generally to a sensor, and more particularly to a pressure gauge and a pressure detecting circuit incorporated in the pressure gauge.
2. Description of the Related Art
There are many pressure gauges, such as U-tube gauge and Bourdon-tube gauge, to measure tire pressure, atmospheric pressure, and water pressure etc.
The U-tube gauge provides water or mercury in a U-shaped tube. The surfaces of the mercury will be at the same level when the pressures on the opposite ends of the U-shaped tube are the same, and there will be a height difference between the mercury surfaces when the pressures are different. One may find the pressure according to the height difference.
A Bourdon-tube gauge has a copper alloy tube, which has an elliptical cross section and is bent into a curved shape. An end of the tube is connected to a connector. The distal end of the tube is closed, and there is a space for the tube to expand. When a pressure is transmitted to the tube through the connector, the curved tube will be extended. A link connects the distal end of the tube and a sector gear. The sector gear is provided with a pointer on a scale to show the value of pressure. In other words, the pressure may deform the tube to move the pointer through the link, and the pressure is directly proportional to the deformation of the tube that the movement of the pointer may indicate the pressure.
There are several drawbacks in the conventional pressure gauges, for example, the U-tube gauge has a poor precision in measurement, and the U-shaped tube usually is made of glass which is easy to be broken. Besides, the temperature in the U-shaped tube will affect the precision of measurement. For the Bourdon-tube gauge the temperature affects the precision of measurement also, and the material fatigue of the copper tube is another big problem.
To improve the conventional pressure gauges, a piezoelectric pressure gauge is provided. The piezoelectric pressure gauge has a piezoelectric material therein. The piezoelectric material may result in electricity from pressure that the piezoelectric pressure gauge may precisely detect pressure.
Temperature has less affection on the piezoelectric pressure gauge, and the piezoelectric pressure gauge may provide a precise measurement. However, the piezoelectric material is exposed under the pressure directly that rusting, moisture and other facts may damage the piezoelectric material. Because the piezoelectric material generates electricity that the piezoelectric pressure gauge cannot be used to sense inflammable gas. In conclusion, there still are some places in the art of pressure measurement that needs to be improved.